1. Field of the Invention
The present invention relates to a hydrogen storage apparatus, and more particularly to a hydrogen storage apparatus for storing a hydrogen storage alloy, such that the efficiency of heat transfer is better when the hydrogen is absorbed or released by the hydrogen storage apparatus, and the hydrogen storage apparatus is safer because the stress imposed on the hydrogen storage alloy is uniform.
2. Description of the Prior Art
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world's oil reserves are rapidly being depleted, the supply of hydrogen remains virtually unlimited. Furthermore, hydrogen, although presently more expensive than petroleum, is a relatively low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of burning hydrogen is water.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of acceptable hydrogen storage medium. Conventionally, hydrogen has been stored in a pressure vessel under a high pressure or stored as a cryogenic liquid, being cooled to an extremely low temperature. Storage of hydrogen as a compressed gas involves the use of large and bulky vessels. Additionally, transfer is very difficult, since the hydrogen is stored in a large-sized vessel; amount of hydrogen stored in a vessel is limited, due to low density of hydrogen. Furthermore, storage as a liquid presents a serious safety problem when used as a fuel for motor vehicles since hydrogen is extremely flammable. Moreover, liquid hydrogen is expensive to produce.
Alternatively, certain metals and alloys have been known to permit reversible storage and release of hydrogen. In this regard, they have been considered as a superior hydrogen-storage material, due to their high hydrogen-storage efficiency. Many metal alloys are recognized as having suitability for hydrogen storage in their atomic and crystalline structures as hydride materials. While this storage method holds promise to be ultimately convenient and safe; improvements in efficiency and safety are always welcome. For example, it is known that heat transfer capability can enhance or inhibit efficient exchange of hydrogen into and out of metal alloys useful in hydride storage systems. As a general matter, release of hydrogen from the crystal structure of a metal hydride requires input of some level of energy, normally heat. Placement of hydrogen within the crystal structure of a metal, metal alloy, or other storage system generally releases energy, normally heat.
The heat released from hydrogenation of hydrogen storage alloys must be removed. Heat ineffectively removed can cause the hydriding process to slow down or terminate. This becomes a serious problem, which prevents fast charging. During fast charging, the hydrogen storage alloy is quickly hydrogenated and considerable amounts of heat are produced. Furthermore, after the hydrogen storage alloy is used for a period of time, some particles may collapse. The collapsed particles will gradually gather at the bottom of the hydrogen storage canister. When the hydrogen storage alloy is hydrided, it will generally expand and the particles at the bottom will swell about 20%, such that the hydrogen storage canister will deform due to non-uniform stress and, often crack. For example, “Hydrogen storage and transportation system” disclosed in U.S. Pat. No. 6,666,034 has the above-mentioned disadvantage.
Furthermore, the hydrogen storage unit disclosed in U.S. Pat. No. 6,626,323 still cannot effectively transfer heat and prevent the particles of the hydrogen storage alloy from shifting. Moreover, in U.S. Pat. No. 6,709,497, since the hydrogen storage structure utilizes at least one heat exchanger tube for transferring heat, the efficiency of heat transfer in the structure is worse, the design of the structure is more complicated, and the cost is higher correspondingly.
Accordingly, the objective of the present invention is to provide a hydrogen storage apparatus for improving the efficiency of heat transfer and the issue of safety, so as to solve the above-mentioned problems.